The aim of this research is to assess the physiological stability of the premature infant while the infant is in the Neonatal Intensive Care Unit (NICU). Our assessment will relate physiological responses to naturally-occurring perturbations to the development of sleep-state organization. We will test the hypothesis that sleep-state organization is protective of the physiological stability of the infant. Investigation of physiological stability entails 1) recording the incidence of apnea, bradycardia, regurgitation of feeds and crying, and 2) monitoring the changing interrelationships (decreased couplings) of heart rate, respiration rate and activity. These "instabilities" will be monitored as they occur following perturbing events which occur in the NICU. These perturbations are feeding (gavage or bottle), receiving baths, taking blood samples and handling of the infant by the experimenter. Sleep state organization will be determined from electrophysiological recordings of heart rate and respiration, time-lapse videotaping of infant behavior, and sensor mattress recordings of infant motility. All monitoring will take place 5 days a week for 23 days. The video-taping of behavior will focus on motility, rapid eye movements, crying, and eyes open or closed. The sensor mattress supplements the video tape analysis by recording state 24 hours a day and scoring the data automatically. Sleep/wake states will be assessed for their periodicity/aperiodicity and the clustering of state variables. The latter will be determined by noting the degree of co-occurrences of the individual state parameters. In addition, a novel application of qualitative dynamics will be used on heart rate, respiration rate and activity to determine the changing nonlinear relationships among these variables. Periodicity/aperiodicity of states will be determined by a series of statistical analyses to determine if sleep cycles are complex or simple, or aperiodic with random or organized transitions (semi-Markovian process). Specifically, we hypothesize that apneas, bradycardias, regurgitation of feeds, and the decrease couplings among physiological variables will be more evident in younger preterm infants whose sleep/wake states are not well organized, and will persist among infants who continue to show during ontogeny decreased clustering of sleep state variables and lack of periodicity of sleep states.